1. Field of the Invention
The present invention relates to an electrical current sensor and a method of manufacturing the electrical current sensor.
2. Description of the Related Art
As an electrical current sensor, there is proposed an electrical current sensor of a type that detects a change in a magnetic field that is generated by an electrical current being measured, by using a magnetic detection element. As such an electrical current sensor, there is a magnetic balance type electrical current sensor having a structure as shown in, for example, FIG. 10A (refer to, for example, WO 2010/143718).
An electrical current sensor 100 shown in FIG. 10A includes a stress relaxation layer 102 and an aluminum oxide (Al2O3) layer 103 provided on a substrate 101, a plurality of magnetic detection elements 104 and an electrode 109 disposed on the aluminum oxide layer 103, a protective film 105 provided on the aluminum oxide layer 103 and the plurality of magnetic detection elements 104 so as to cover the magnetic detection elements 104, a plurality of coils 106 disposed on the protective film 105, a protective film 107 provided on the protective film 105 and the plurality of coils 106 so as to cover the coils 106, and a shield layer 108 disposed on the protective film 107.
The respective members constituting the electrical current sensor 100 are formed by laminating in order from the stress relaxation layer 102 on the substrate 101. Further, the shield layer 108 is formed to a thickness of 15 μm or more by, for example, a plating method.
In the electrical current sensor 100 shown in FIG. 10A, in order to form the shield layer 108 over the plurality of coils 106, it is necessary to form the protective film 107 (an insulating film) on the coils 106 and then form the shield layer 108 on the protective film 107. Further, in order to enhance the effects of the shield layer 108 of shielding a magnetic field being measured, and to strengthen the cancellation effects of the coils 106, it is necessary to make the protective film 107 thinner, thereby bringing the coils 106 and the shield layer 108 close to each other.
However, if the protective film 107 is made thinner, there is a problem in that the upper surface of the protective film 107 (the lower surface of the shield layer 108) has ripples formed by the shapes of the coils 106 (refer to FIG. 10B). Further, if the protective film 107 is made thinner, there is a problem in that cracks are easily generated in the protective film 107 due to the stress of the shield layer 108. If the magnetic detection element 104 is corroded due to absorption of water such as moisture through the cracks, the reliability of the electrical current sensor 100 is affected.
In addition, in the electrical current sensor 100 shown in FIG. 10A, in order to prevent warping of the substrate 101 due to the stress of the shield layer 108, it is necessary to provide the stress relaxation layer 102 on the substrate 101.